This invention relates to a light-level monitoring system for monitoring the level of light in a distant location or in a plurality of distant locations from a central location. The present invention is particularly useful when coupled with a controller for adjusting the power to light fixtures in the monitored areas.
The need to regulate and conserve energy by automatically controlling lighting is well known. In an automatic lighting control system a controller adjusts the power to a light fixture in response to a signal from a light-level monitor. In the prior art most monitoring and control systems are localized systems controlling one or a few light fixtures. Each localized system requires a light-level monitor, a controller, and generally a power supply. Therefore, the monitor and controller must be of a very unsophisticated nature to reduce costs. Therefore, it is desirable to have a centralized monitoring system wherein a multiplicity of light-level sensors are coupled to a single power supply and controller.
It is further desirable to have a centralized monitoring system wherein the signal to the controller representing the light-level at each location is linearly proportional to the light-level at that location and bears a known relationship to the light level. With such information, the controller may always be aware of the true light-level in each location and can easily make adjustments as required.
It is further desirable that the signal-to light-level ratio of all of the signals at the control unit be identical. If this is true, the controller needs only to use one method of interpreting the signals to determine the light level signified.
It is also desirable that the signal from the local light sensors to the control unit be of high enough order than any electrical "noise" or "smog" not affect the resolution.
It is further desirable that the installation of such a system be simple so that it may be accomplished by a layman or, at most, by an electrician and not require an electronic technician.
It is further desirable that the system is readily adaptable to incorporate "Contrast Control" as disclosed in U.S. Pat. No. 4,229,664 for PHOTOELECTRIC METHODS AND APPARATUS FOR REGULATING ELECTRICAL POWER CONSUMPTION IN STORES, issued Oct. 21, 1980.